1. Field of the Invention
The present invention is related to an epi-structure of a light-emitting device, especially related to an epi-structure having a plurality of uneven multiple quantum well (MQW) applied to a light-emitting device.
2. Background of the Related Art
It is known that light in all direction is emitted by the active layer of a light-emitting device (Light-Emitting Device; LED), and the efficiency of a LED may be acquired by the following equation:Eeff=Ei(internal)*Ee(external)
where Ei represents the internal efficiency from an active layer and Ee represents the external efficiency.
Typical efficiency improvement of a LED focuses on the improvement of external efficiency, for example, FIG. 1A from US Publication No. US20050082562A1, FIG. 1B form US Publication No. US20050277218A1, FIG. 1C from US Publication No. US20040104672, FIG. 1D form US Publication No. 6900473 and US67777871. The improvement aforementioned focus on the surface of a LED by forming uneven surface (by etching) on the external side of a LED to prevent light in a chip from total reflection, so as to enhance external efficiency Ee. Accordingly, Ee is enhanced reached 80%, which is physical limitation.
Typically, the Ei from an internal active layer is reached about 40%. The whole efficiency Eeff of a LED may be improved by enhancing Ei. Accordingly, the present invention provides the active layer of a LED with uneven multiple quantum well. The volumetric area of uneven MQW is more than a conventional smooth MQW, which may enhance the Ei from an internal active layer and further improve the whole efficiency Eeff of a LED.